Single Donor Kit cars
(The thread title should have read "Cat C or Cat D donor".)
I have had a reply from the DVLA to my enquiry about a single donor vehicle and it is all dealt with in leaflet INF26 "The registration of Rebuilt or Radically Altered Vehicles and Kit Cars" dated October 2015.
As far as I can see, for cars such as a 250 replica made by Tribute Automotive on a BMW Z3 donor, this will come under section 5 "Kit Conversions" and I quote "This is where a kit of new parts is added to an existing vehicle... The general appearance of the vehicle will change and result in a different description being put on the Vehicle Registration Certificate (V5C)." and later "A vehicle will keep the registration number of the original vehicle if the original unaltered chassis/monocoque bodyshell has been used." otherwise, "The vehicle must have an IVA. The date of manufacture will be taken from the IVA certificate."
Section 2 "Vehicles that have been rebuilt using a mix of new and/or used parts" says "To keep the original registration number, cars must use the original UNALTERED chassis or monocoque bodyshell." (my capitals) so surely this does not apply.
The case of the Z3 where all external panels can be unbolted and replaced appears to be outside their consideration.
I would be interested to hear from anyone who has built one of these kits and their experience of registering or taxing them. Have the Police stopped you and asked to see the V5C?